1. Field of the Invention
The present invention relates to a method of continuous rolling by means of welding billets before rolling, and an apparatus therefor, and particularly relates to a method and an apparatus applying induction-heating treatment to the welded billets.
2. Description of the Related Art
A known continuous rolling method to produce wire, rod, or shape steel with energy-saving and high efficiency comprises the steps of discharging billets from a reheating furnace one at a time, welding the rear end of a preceding billet with the front end of a succeeding billet by a single unit travelling flash-butt welder, removing the burr on the welded portions using a scarfer or the like, reheating thus formed continuous billet to a temperature necessary for rolling by a stationary induction-heating unit, then rolling the continuous billet in a rolling mill line: (disclosed in, for example, unexamined Japanese patent publication No.52-43754(1977)).
There is an another continuous rolling method in which billets discharged from a reheating furnace are joined together by a single unit travelling flash-butt welder to form a continuous billet, and the continuous billet is reheated again in the reheating furnace, followed by being rolled: (disclosed in, for example, examined Japanese patent publication No.52-11722(1982)).
The inventors of the present invention previously proposed a hot direct rolling method (hereinafter referred to simply as "HDR") for rolling the billets directly sent from a continuous casting machine. In the HDR method, induction-heating is applied for reheating treatment of the billets. The induction-heating aims at:
(1) Reheating the billets during a period from cutting thereof in the continuous casting machine (hereinafter referred to simply as "CCM") to direct feeding thereof to the inlet of a rolling mill line; PA1 (2) Reducing the temperature difference between front end and rear end of billets produced at cutting thereof in CCM, (temperature distribution is induced from time difference after casting).
These aims have been achieved by changing electric power given to a stationary induction-heating unit depending on inlet temperature of billet or by changing running speed of billet.
When continuously rolling billets that are not only reheated in a reheating furnace but also directly fed from CCM, it is very difficult by a stationary reheating method to uniform the induced temperature distribution. In addition, the running speed of billets cannot be changed through a heating unit in a continuous rolling method.